Interpretive Summary: Invasive plant species damage natural areas, alter ecosystem processes, displace native species, hybridize with natives, and support other potentially damaging plants, animals, and pathogens. To begin to assess the environmental and physiological factors that contribute to the potential "invasiveness" of plant species, the influence of light and temperature on germination was determined for the Florida non-native, ornamental Mexican petunia (Ruellia tweediana) and Florida native wild petunia (Ruellia caroliniensis), and growth under wet and dry conditions was investigated. More seeds of wild petunia germinated at lower temperatures under light as compared to Mexican petunia. Under wet or dry conditions, Mexican petunia utilized nitrogen and phosphorous more efficiently (i.e., grew more than wild petunia per unit nitrogen and phosphorous).

Technical Abstract:
Invasive species have disrupted thousands of acres of natural areas in Florida alone and appear to have a physiological competitive advantage over native species. The influence of light and temperature on germination was determined for the potentially invasive Mexican petunia (Ruellia tweediana Griseb.) and native wild petunia (Ruellia caroliniensis Steud.). Seeds were collected and germinated in incubators with light or darkness at 10, 15, 24, and 30/20 degrees centigrade. Provision of light generally did not increase germination for either species, except at 24 degrees centigrade (R. caroliniensis) and 33 degrees centigrade (R. tweediana). For R. caroliniensis, highest germination (86-94%) occurred at 33 degrees centigrade and 30/20 degrees centigrade, and for R. tweediana, highest germination (98-100 percent) occurred at 30/20 degrees centigrade. Studies were also initiated to determine whether the potentially invasive species has a competitive advantage over the native species when grown under wet and dry hydrologic conditions. Growth and development measurements after 8 weeks under controlled conditions indicate that R. tweediana had lower specific leaf area when grown in wet or dry conditions, and lower specific stem length when grown in wet conditions, as compared to R. caroliniensis. Throughout the experiment, net CO2 assimilation was consistently lower for R. caroliniensis grown under dry or wet conditions, in comparison to R. brittoniana. Likewise, utilization of nitrogen and phosphorus was lower for R. caroliniensis than R. brittoniana, regardless of moisture conditions. For shoot nutrient content, significant species x moisture interactions occurred for measured phosphorus (P), calcium (Ca), zinc (Zn), copper (Cu), and sodium (Na). For root nutrient content, significant species x moisture interactions occurred for measured potassium (K) and iron (Fe).